Methyl tert-butyl ether (MTBE) is a synthetic compound produced almost exclusively for use in gasoline as an octane enhancer and lately as a fuel oxygenate to reduce atmospheric concentrations of carbon monoxide and ozone in accordance with the United States Clean Air Act Amendments of 1990. Several other chemicals have also been used as fuel oxygenates, including ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), diisopropyl ether (DIPE), tert-butyl alcohol (TBA), methanol, and ethanol (Johnson, R.; Pankow, J.; Bender, D.; Price, C.; Zogorski, J. MTBE, To what extent will past releases contaminate community water supply wells? Environ. Sci. Technol. 2000, 34, 210A-217A). Because of its low cost, ease of production, and favorable transfer and blending characteristics, MTBE is the most commonly used fuel oxygenate (Ainsworth, S. Oxygenates seen as hot market by industry. Chem. Eng. 1992, 70, 26-30; Shelly, S.; Fouhy, K. The drive of cleaner burning fuel. Chem. Eng. 1994, 101, 61-63; and Squillace, P. J.; Pankow, J.; Korte, N. E.; Zogorski, J. S. Environmental Behavior and Fate of Methyl tert-Butyl Ether (MTBE), U.S. Geological Survey, FS-203-98, 1998). MTBE is currently the focus of public concern, particularly in the United States, as MTBE has been detected in groundwater and surface water across the U.S. (Squillace, P. J.; Zogorski, J. S.; Wilber, W. G.; Price, C. V. Preliminary assessment of the occurence and possible sources of MTBE in groundwater in the United States, 1993-1994. Environ. Sci. Technol. 1996, 30, 1721-1730 and Reuter, J. E.; Allen, B. C.; Richards, R. C.; Pankow, J. F.; Goldman, C. R.; Scholl, R. L.; Seyfried, J. S. Concentrations, sources, and fate of the gasoline oxygenate methyl tert-butyl ether (MTBE) in the multiple-use lake. Environ. Sci. Technol. 1998, 32, 3666-3672). MTBE has a very low taste and odor threshold, and thus even small quantities of MTBE will affect the quality of drinking water. There is also concern about its possible risk to human health, which is still inconclusive.
Generally, contaminants can be naturally attenuated by various processes, including volatilization, adsorption, dispersion, hydrolysis, and biodegradation. Unlike other gasoline components, such as BTEX compounds (benzene, toluene, ethylbenzene, o-, m-, p-xylene), MTBE is very water-soluble and it tends to partition from gasoline to the water phase. Once dissolved in water, the relatively low Henry's law constant of MTBE does not lead to significant losses by partitioning in to the gas phase. The relatively low Koc of MTBE implies that its movement is minimally retarded by soil particles, thus allowing MTBE plumes to travel at almost the same velocity as the groundwater stream. The reduction of MTBE mass by physical processes in groundwater is probably insignificant, because volatilization in aquifers is not very efficient and the hydrolysis of MTBE at almost neutral pH values is very slow (O'Reilly, K. T.; Moir, M. E.; Taylor, C. D.; Smith, C. A.; Hyman, M. R. Hydrolysis of tert-butyl methyl ether (MTBE) in dilute aqueous acid. Environ. Sci. Technol. 2001, 35, 3954-3961). Therefore, bioremediation may play a significant role in mass reduction of MTBE at contaminated sites.
Although early reports indicated that MTBE is resistant to biodegradation, aerobic MTBE biodegradation has been clearly demonstrated (Deeb, R. A.; Scow, K. M.; Alvarez-Cohen, L. Aerobic MTBE degradation: an examination of past studies, current challenges and future research directions. Biodegradation 2000, 11, 171-186; Fayolle, F.; Vandecasteele, J. P.; Monot, F. Microbial degradation and fate of methyl tert-butyl ether and related fuel oxygenates. Appl. Microbiol. Biotechnol. 2001, 56, 339-349; and Stocking, A. J.; Deeb, R. A.; Flores, A. E.; Stringfellow, W.; Talley, J.; Brownnell, R.; Kavanaugh, M. C. Bioremediation of MTBE: a review from a practical perspective. Biodegradation 2000, 11, 187-201) along with the biodegradation of other structurally related fuel oxygenates such as TAME, ETBE, and TBA. Recently, MTBE has also been shown to be biodegradable anaerobically under methanogenic (Mormile, M. R.; Liu, S.; Suflita, J. M. Anaerobic biodegradation of gasoline oxygenates: extrapolation of information to multiple sites and redox conditions. Environ. Sci. Technol. 1994, 28, 1727-1732 and Wilson, J. T.; Soo Cho, J.; Wilson, B. H.; Vardy, J. A. Natural Attenuation of MTBE in the subsurface under methanogenic conditions, U.S. Environmental Protection Agency, Office of research and Development: Washington, D.C., 2000), denitrifying (Bradley, P. M.; Chapelle, F. H., Landmeyer, J. E. Methyl t-butyl ether mineralization in surface water sediment microcosms under denitrifying conditions. Appl. Environ. Microbiol. 2001, 67, 1975-1978), iron (III) reducing (Finneran, K. T.; Lovley, D. R. Anaerobic degradation of methyl tert-butyl ether (MTBE) and tert-butyl alcohol (TBA). Environ. Sci. Technol. 2001, 35, 1785-1790), and sulfate-reducing (Somsamak, P.; Cowan, R. M.; Häggblom, M. M. Anaerobic biotransformation of fuel oxygenates under sulfate-reducing conditions. FEMS Microbiol Ecol. 2001, 37, 259-264) conditions. tert-Butyl alcohol (TBA) is often detected as intermediate of MTBE biodegradation, suggesting that cleavage of the ether bond is the initial step in the degradation pathway. Under both aerobic and anaerobic conditions, the slow degradation of TBA indicated by an enrichment of these components suggests that the degradation of the metabolite is a crucial step in MTBE mineralization.
Anaerobic MTBE degradation is extremely important for natural attenuation as a remediation option, since MTBE contaminated sites are often subsurface with limited oxygen available for biodegradation. Moreover, co-contamination with a mixture of gasoline hydrocarbons leads to a rapid consumption of oxygen in aquifers. Under anaerobic conditions, MTBE degradation is relatively rare.
The present invention relates to the discovery of the ability of MTBE-utilizing cultures to metabolize O-methyl substituents of plant phenolic compounds and to the effect of these compounds on anaerobic MTBE degradation.